- Your Online Learning Center

New Video Lectures are added. Must watch Click Here

The Solar Syastem

Study Material > Geography
  • The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun.
  • The Solar System is located in the Orion Arm, about two-thirds of the way out from the center of the Milky Way.
  • TheAndromeda Galaxy, also known as Messier 31, M31, or NGC 224, is a spiral galaxy approximately 780 kiloparsecs (2.5 million light-years) from Earth. It is the nearest major galaxy to the Milky Way and was often referred to as the Great Andromeda Nebula in older texts.
  • The sun’s nearest known star is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away. Proxima Centauri forms a third component of the Alpha Centauri star System.
  • Alpha Centauri is the closest star system to the Solar System, It consists of three stars: Alpha Centauri A and Alpha Centauri B, which form the binary star Alpha Centauri AB, and a small and faint red dwarf, Alpha Centauri C (also named Proxima Centauri.

The Sun

  • TheSun is the star at the center of the Solar System.  It is by far the most important source of energy for life on Earth.
  • Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System.
  • About three-quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen-carbon, neon, and iron. 
  • The part of the Sun that we can see is known as Photosphere. The temperature at the photosphere is about 6000 degree Celsius. The temperature at the center is about 15 million degree Celsius.
  • The Chromosphere is the second outermost layer of the Sun’s atmosphere, which is only visible to the naked eye during a solar eclipse. The Chromosphere is notable for being hotter than the photosphere, the next layer towards the Sun.
  • The Chromosphere is located between the photosphere and the corona.
  • The outermost part of Sun which is visible only at the time of a solar eclipse is known as
  • A storm of hot atoms which dissipates from the Photosphere of the Sun, overcomes its gravity and goes into the outer space, is known as Solar Flares.
  • The regions from where solar flares originate, some dark spots are seen, these are called Sun Spots.
  • The spots are relatively colder regions of the Sun, having temperatures of about 1500 degree Celsius.
  • Solar Cycle: The amount of magnetic flux that rise up to the Sun’s surface varies with time in a cycle called the Solar Cycle or Sun Spot Cycle. Solar cycle is 11 year cycle covering the maxima and minima.  

  • Sunspot maxima correspond generally to the periods of higher solar activity.
  • These activities includes increased solar wind and phenomenons like Aurora and Magnetic Storms.
  • Sunspot minima has no activities and Sun can be referred as ‘Quiet Sun’.


  • The definition of Planet set in 2006 by the International astronomical Union(IAU) states that in the solar system a planet is a celestial body that
    1. Is in Orbit around the sun
    2. Has sufficient mass to assume hydrostatic equilibrium(a nearly round shape).
    3. Has “cleared the neighbourhood” around its Orbit.
  • There are eight planets which are revolving around the Sun in elliptical path. These planets in the order of increasing distance of the Sun are: Mercury, Venus, Earth, mars, Jupiter, Saturn,Uranus, Neptune.


  • Mercuryis the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 88 days is the shortest of all the planets in the Solar System. It is named after the Roman deity Mercury, the messenger to the gods.
  • Mercury's axis has the smallesttilt of any of the Solar System's planets (about  1⁄30 degree)
  • Mercury has been now been visited by two spacecraft, Mariner 10 and MESSENGER.
  • There is no atmosphere and water on the surface of the mercury and hence there is no possibility of life on this planet.


  • Venusis the second planet from the Sun and the sixth largest., orbiting it every 224.7 Earth   It has no natural satellites. It is named after the Roman goddess of love and beauty. Venus' orbit is the most nearly circular of that of any planet, with an eccentricity of less than 1%.
  • Its mass, density and radius are comparable to those of Earth. Hence, it is called Earth’s twin.It is radically different from Earth in other respects. It has the densest atmosphereof the four terrestrial planets, consisting of more than 96% carbon dioxide. The atmospheric pressure at the planet's surface is 100 times that of Earth.
  • It is the brightest Planet of the Solar system and is the second-brightest natural object in the night sky after theMoo
  • Venus is the only planet whose period of rotation (243days) is longer than the period of revolution (225 days) around the Sun. Unlike all other planets, Venus and Uranus revolve around the Sun from East to West.
  • Since, Venus is seen in the East in the morning and in the west in the evening, it is called Morning Star as well as Evening Star.
  • Its one side is always facing the Sun and its surface temperature is always 450 degree Celsius. There is no possibility of life on this planet.
  • It does not possess any satellite. It can be seen with naked eyes.
  • The first spacecraft to visit Venus wasMariner 2 in 1962. Mariner-10 and Messenger are the artificial satellites which surveyed the surface of the Mercury.
  • Venus has no magnetic field, perhaps because of its slow rotation. Venus has no known satellites.


  • It is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets. The Earth is the densest major body in the solar system.
  • Earthrotates about its axis over 365 times; thus, an Earth year is about 365.26 days long. Earth's axis of rotation is tilted, producing seasonal variations on the planet's surface.
  • There is atmosphere and water on the surface of the Earth and so life is there on the Earth’s surface.
  • Astronomers call the distance from the Sun To earth (93 million miles/150 million Km) an Astronomical unit9(AU) and use it to measure planetary distances.
  • Average temperatures and air pressures on Earth allow liquid water to collect on the surface, a unique feature among planets within the solar system.
  • Earth’s atmosphere mostly nitrogen and oxygen and a strong magnetic field protect the surface from harmful solar radiation. These are the condition that nurture life.
  • The earth looks blue when seen from the outer space due to the presence of large amount of water hence it is called blue planet.
  • A single natural satellite, the moon, orbits Earth, probably created by a collision with a huge planetesimal more than 4 billions years ago. Its distance from the Earth is 84 x 105 Km. Its mean diameter is 7.35 X 1022 Kg.
  • It revolves around the Earth in 27.3 days. It emits electromagnetic waves in the radio wave region, hence it is called radio moon. The moon always keeps the same face towards the Earth.
  • The temperature of the Moon During the day is 100o C and at night is 150o. The surface of the Moon has craters.
  • There is no atmosphere and water on the Moon’s surface and hence there is no possibility of life.


  • Full moon can be seen only once in about a month’s time.
  • Full moon night or Poornima. A fortnight later, it is a New moon night or Amavasya.




  • Marsis the fourth planet from the Sun and the second-smallest(Seventh largest) planet in the Solar System, after Mercury. Named after the Roman god of war, it is often referred to as the "Red Planet" because the iron oxide prevalent on its surface gives it a reddish appearance.  Mars is a terrestrial planet with a thin atmosphere mostly consisting of Carbon dioxide. There are white patches on its surface, which shrink in summer and expand in winter. Mars changes colour in different season.
  • Mars is tilted at 23o in the same way as the Earth, so experience four seasons as Earth. Like Earth, Mars has polar ice caps, although those on Mars are made up mostly of carbon dioxide ice (dry ice), while those on Earth are made up of water ice.
  • Mars has twotiny moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids. Mars can easily be seen from Earth with the naked eye.
  • Though Mars is much smaller than Earth, its surface area is about the same as the land surface area of Earth.
  • Mars is called the red planet because of its red appearance due to presence of iron .
  • Mars has some of the most highly varied and interesting terrain of any of theterrestrial planets, some of it is quite spectacular:
    1. Olympus Mons: The largest volcano and second-highest known mountain in the Solar System. Tharsis: a huge bulge on the Martian surface that is about 4000 km across and 10 km high.
    2. Valles Marineris: One of the largest canyons in the Solar System.
    3. Hellas Planitia: an impact crater in the southern hemisphere over 6 km deep and 2000 km in diameter.


  • Jupiteris the fifth planet from the Sun and the largest in the Solar System. The Romans named it after their god Jupiter. Jupiter is the fourth-brightest object in the night sky after the Sun the Moon and Venus. Jupiter is primarily composed of 93 %  hydrogen 7 % helium.
  • The mass of Jupiter is 318 times that of Earth. It gives of more energy than it receives from the Sun, because of heat inside it. Jupiter, along with Saturn, Uranus, and Neptune is classified as a gas giant.
  • In 1610 Galileofirst discovered Jupiter's four large moons Io, Europa, Ganymede and Callisto (now known as the Galilean moons).
  • Jupiter was first visited byPioneer-10 in 1973 and later by Pioneer-11, Voyager-1, Voyager-2 and Ulysses. The spacecraft Galileo orbited Jupiter for eight years. It is still regularly observed by the Hubble Space Telescope.
  • What is the Great Red Spot on Jupiter made out of?
    1. The Great Red Spot is a giant, spinning storm in Jupiter's atmosphere. It is like a hurricane on Earth, but it is much larger. Jupiter's Great Red Spot is more than twice the size of Earth! Winds inside this storm reach speeds of about 270 miles per hour.
  • When it is in the nighttime sky, Jupiter is often the brightest "star" in the sky (it is second only to Venus, which is seldom visible in a dark sky). The four Galilean moons are easily visible with binoculars; a few bands and the Great Red Spot can be seen with a small astronomical telescope.
  • Jupiter has 67 known satellites


  • Saturnis the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius about nine times that of Earth. Saturn is named after the Roman god of agriculture; its astronomical symbol .
  • Like Jupiter, Saturn has about 75% hydrogen and 25 % helium with traces of water, methane, ammonia and rock. Saturn is the least dense of the planets; its specific gravity (0.7) is less than that of water.
  • Two prominent rings ( A and B) and one faint ring (C) can be seen from the Earth, Though they look continous from the Earth, the rings are actually composed of innumerable small particles each in an independent orbit. They range in size from a centimeter or so to several meters.
  • The rings are extraordinarily thin they are 250000 Km or more in diametrer and less then one Km thick.
  • Saturn was first visited by NASA'sPioneer 11 in 1979 and later by Voyager 1 and Voyager 2. Cassini (a joint NASA / ESA project) arrived on July 1, 2004 and orbits Saturn for four years.
  • Saturn has 62 known satellites.


  • Uranus is named after the greek God of Sky. Uranus is the seventh planet from the Sun and the third largest (by diameter). Uranus is larger in diameter but smaller in mass than Neptune. Uranus is similar in composition to Neptune, and both have different bulk chemical composition from that of the larger gas giants Jupiter and Saturn. For this reason, scientists often classify Uranus and Neptune as "ice giants" to distinguish them from the gas giants.
  • Uranus'satmosphere is similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, but it contains more "ices" such as water, ammonia, and methane, along with traces of other hydrocarbons. It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49 K. The interior of Uranus is mainly composed of ices and rock.
  • Uranus is the first planet discovered in modern times and was discovered by William Heschel.
  • Most of the planet spin on an axis nearly perpendicular to the plane of the ecliptic but Uranus axis is almost parallel to the ecliptic. This results in the odd fact that Uranus Polar Regions receive more energy input from the Sun than do its equatorial regions.
  • Its atmosphere has about 83% hydrogen, 15% helium and 2 % methane. Uranus blue colour is the result of absorption of red light by methane in the upper atmosphere. Like the other gas planets, Uranus has rings.
  • Uranus has been visited by only one spacecraft, Voyager 2 on Jan 24 1986.
  • Like the othergas planets, Uranus has  Like Jupiter's, they are very dark but like Saturn's they are composed of fairly large particles ranging up to 10 meters in diameter in addition to fine dust. There are 13 known rings, all very faint; the brightest is known as the Epsilon ring. Uranus has 27 known satellites.


  • Neptune is the eighth planet from theSun and the fourth largest (by diameter). Neptune is smaller in diameter but larger in mass than Uranus. It is 17 times the mass of Earth.
  • Neptune is named after Roman god of the Sea. Neptune has 14 known satellites.
  • Neptune has been visited by only one spacecraft, Voyager 2 on Aug 25 1989. 
  • Neptune's blue color is largely the result of absorption of red light by methane in the atmosphere but there is some additional as-yet-unidentified chromophore which gives the clouds their rich blue tint.
  • Like Jupiter and Saturn, Neptune has an internal heat source -- it radiates more than twice as much energy as it receives from the Sun.
  • Neptune also has Like Uranus and Jupiter, Neptune's rings are very dark but their composition is unknown.


  • Pluto is no longer considered a planet in our solar system. Pluto orbits beyond the orbit of Neptune. It is much smaller than any of the official planets and now classified as a Dwarf planet.
  • It is the second largest Dwarf Planet in the solar system. In Roman mythology, Pluto is the god of the underworld. Pluto orbits beyond the orbit of Neptune (usually).
  • All the planets orbit the Sun in or nearly the same plane, called the ecliptic. Dwarf planet Pluto’s orbit is the most highly inclined (18 degree). Because of this, for part of its orbit, Pluto is closer to the Sun than Neptune.

 Regions of the Solar Syatem

  • The Solar System is divided into two main regions:
    1. The inner planets
    2. The outer planets.
  • The inner planet consist of the four rocky, or terrestrial planets, Mercury, Venus, Earth and Mars, while the outer planets consists of the two gas giant planets, Jupiter, Saturn, and the two ice giant planets, Uranus, and Neptune. The asteroid belt divides these two regions.
  • The inner planets are composed mainly of rocky materials such as silicates in their outer crusts and mantles and metals such as iron and nickel in their in their inner cores. The outer planets are composed mainly of gases such as hydrogen and helium.
  • Beyond the orbit of the last planet, Neptune, lies two regions known as the Kuiper belt and the Oort cloud. The Kuiper belt is the home of dwarf planets and other small, planet­ like bodies. Much farther out, the Oort cloud is the home of the icy comets. Very little is known about the objects in these two regions

Terrestrial planets

  • The term terrestrial is derived from the Latin word 'terra', which means earth. Thus, terrestrial planets can be described as planets that are earth-like in nature, meaning those that are similar in composition and structure to that of the earth. They are also known as 'telluric planets' or 'rocky planets'.These are Mercury, venus, Earth and Mars.
  • Terrestrial planets usually have a metallic core - consisting mostly of iron - and a silicate mantle. They have topological features like mountains, volcanoes, valleys, craters, etc. on their surface. Unlike giant planets (which have a primary atmosphere), terrestrial planets have a secondary atmosphere. Terrestrial planets are known to have few or no satellites of their own. For example: Earth has only one satellite, Mars has two, whereas Mercury and Venus have none.
  • All four planets have volcanoes, which long ago spewed out gases that created atmosphere on all but Mercury , which is too close to the Sun to hold onto an atmosphere. Mercury and Venus are called Interior planets.


  • These are group of more than 1600 tiny rock pieces moving around the Sun in between Mars and Jupiter.
  • The largest amongst them is called ceres with a radius of 350 km while the smallest one is just 50 m in radius.
  • Asteroids are believed to be the pieces of a much larger planet, which broke up due to gravitational pull of Jupiter.
  • The density and chemical composition of asteroids is similar to that of the Moon.
  • The largest asteroid completes one Revolution around the sun in 4.6 years. Asteroid belt is a broad ringe of 2 to 3.3 AU from the Sun. This belt is composed of space rocks as small as dust grains and as large as 600 miles (1000 Km) in diameter.
  • Asteroids are made of minerals compounds, especially those containing iron, carbon and silicon. Although the Asteroid belt contains enough material for a planet one did not form there because Jupiter's gravity prevented the asteroids from crashing together.
  • The belt seperates the first region of the solar system from the second. Asteroids when comes under the influence of Earth's gravity, they move with great velocity towards Earth and appears as a streak of light called Meteors.
  • Meteors due to collision with the particles of the atmosphere burn and get converted into ashes. Meteors which are large in size do not burn completely and reach the surface of the earth are called Meteorites.

The Giant planets

  • Second region belongs to the gas giants Jupiter, Saturn, Uranus and Neptune. The closest Jupiter is 5.2 AU from the sun and the most distant Neptune is 30.11 AU. Jupiter is the largest planet in the solar system, its diameter is 109 times larger than Earth’s.
  • The giant planets have solid cores, but most of their immense size is taken up by hydrogen, helium and methane gases that grow thicker and thicker until they are like sludge near the core.
  • On Jupiter, Saturn, and Uranus the gases form wide bands over the surface e.g., the Great Red Spot of the Jupiter. These planets have such strong gravity that each has attracted many moons to orbit it.
  • Jupiter has the most Moons at least 64 and Neptune has the fewest 8 but Neptune's Moon Titan is the largest of all. Jupiters four large moons called the Galilean Moons (Io, Europa, Ganymede and callisto).
  • Most Moons are balls of Ice and rock, but Jupiter's Europa and saturns Titan may have liquid water below ice bound surfaces.
  • Additional, the giant planets have rings of broken rock and ice around them, no more than 330 feet (100 meters) thick. Saturn's hundreds of rings are the brightest and most famous.
  • Uranus is tilted at 90o so it almost rolls around the sun. Hence it is also called as lying planet. Uranus is green in appearance due to presence of Methane.

The Kuiper Belt

  • The third region of the solar system, the Kuiper belt contains the dwarf planet Pluto. Pluto has a single moon, Charon. Pluto does not Orbit on the same plane, called the ecliptic, as the rest of the planets do.
  • Instead, its Orbit diverges more than 170 C above and below the ecliptic. It’s orbit’s oval shape brings Pluto within the orbit of Neptune for a large percentage of its long year, which is equal to 248 Earth years.
  • Two thirds the size of the earth's moon Pluto has a thin, frigid Methane atmosphere. Charon is half Pluto’s size and orbits less than 32000 miles from Pluto surface. Because of the closeness in the sizes of Pluto and Charon, some astronomers consider them to be a double Planet.
  • The Kuiper belt holds asteroids and the “short period” comets that pass by Earth in orbits of 20 to 200 years. These bodies are the remains of planet formation and did not collect into planets because distances between them are too great for many collisions to occur.
  • Most of them are loosely compacted bodies of Ice and mineral-Dirty Snowballs. An estimated 200 million Kuiper belt objects Orbit within a band of space from 30 to 50 AU from the Sun.

The Oort Cloud

  • The Oort Cloud is a theoretical spherical cloud of predominantly icy planetesimals that is believed to surround the sun. It is also a collection of comets- as many as two trillion, scientists calculate.
  • The outer edge of the Oort cloud marks the farthest reach of the Sun’s gravitational power to bind bodies to it.


  • Comets are composed of Rock like materials surrounded by large masses of easily vaporized substances like ice, water, ammonia and methane.
  • They revolve around the sun in highly elliptical orbits and are not visible ordinarily. Their time period of revolution around the Sun is very high. Comets appear to have a bright head and a long tail while passing close to the Sun. When a Comet is far away from the Sun, it shows no tail. When a comet approaches the Sun, some of its material is evaporated due to heat of the Sun. The light of the Sun exerts a pressure on these vapours and forces them away from the comet in the form of its tail.
  • Periodic Comets are often written with a prefix, which is determined after the second perihelion passage and some of the comets in this category are still unnumbered.
  • The letter P written after the number indicates that the comet is periodic. Most comets are named after the people who discovered them and others take the names of those who calculated the orbital periods that some of them engaged in a lifelong career of computing these values.
  • Some of the most popular periodic comets are Halley, Encke, Temple-Tuttle and Swift-Tuttle.
  • Dead Comets: Once a comet has out-gassed all the available volatile, its coma and tail will disappear and the remaining inert nucleus will take on the appearance of a low albedo asteroid. After 500 times or so a comet passes near the Sun, most of its ice and gas is lost, leaving a rocky object.
  • They have highly elliptical orbits that bring them very close to the Sun and swing them deeply into space, often beyond the orbit of Pluto. Comet develop a surrounding cloud of diffused material, called as coma, that usually grows in size and brightness as the comet approaches the Sun.
  • Solar wind is responsible for the formation of tails since solar winds goes away from the Sun. Usually a small, bright nucleus(less than 10 Km in diameter) is visible in the middle of the coma.
  • Halley's Comet had been observed since more than 2000 years ago. Meteor shower sometimes occurs when the earth passes through the orbit of a comet.


  • Meteors are the smaller pieces of stones and metals, which may be produced due to breaking up of comets while approaching the Sun.
  • When these pieces come close to the Earth, they get attracted towards Earth and burn due to friction of the atmosphere and look like a bright line of fire. The light so produced is visible even from the surface of Earth.
  • Such bright meteors are called Fireballs or Shooting Stars. Sometimes, the large pieces do not burn completely and reach the surface of the Earth as stony iron balls resulting in craters on the Earth surface. These are called meteorites. A shooting star is another name for a meteoroid that burns up as it passes through the Earth's atmosphere.
  • most of the shooting stars that we can see aromas meteoroids these are objects as a smallest piece of sand and as large as LDA smaller than a piece of if they are larger than about astronomers call them asteroids.


  • A large group of stars is called Galaxy. There are large number of galaxies having different sizes- regular and irregular shape. Galaxies can be divided into two categories

Normal Galaxies

  • This Galaxies emit comparatively small amount of radio radiations as compared to the total radiations emitted. This Galaxies are bright from the centre and gradually dim towards the edges. Each normal Galaxy contains billions of stars in the form of a band, travelling together in the universe.
  • Depending upon their shapes the normal galaxies may be divided into three groups namely
    1. Eliptical Galaxy
    2. Spiral galaxy
    3. Irregular Galaxy
  • About 18% of the Galaxies are elliptical, 80% of the Galaxies are spiral and only 2% of the Galaxies are irregular Galaxy. The irregular Galaxies are youngest, spiral Galaxies are middle aged and elliptical Galaxies are quite old.

Radio galaxies

  • These Galaxies emit million times more radio radiations than normal Galaxy. The radio radiations do not comes from the Galaxy itself but are believed to be coming from two large radio sources.

Milky Way

  • Milky way is the name of the Galaxy to which our earth belongs.
  • The Milky way is the glowing belt of the sky formed by the combined light of a very large number of stars. If one looks at the sky on a clear night, a hazy band of white light stretching across a great circle is seen, which is called the Milky Way Or Akash Ganga.
  • It is so called because the light from the various stars together gives the impression of a stream of milk flowing across the sky.

Transit of Venus

  • A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and a superior planet, becoming visible against (and hence obscuring a small portion of) the solar disk.
  • During a transit, Venus can be seen from Earth as a small black disk moving across the face of the Sun. The duration of such transits is usually measured in hours (the transit of 2012 lasted 6 hours and 40 minutes). A transit is similar to a solar eclipse by the Moon. While the diameter of Venus is more than 3 times that of the Moon, Venus appears smaller, and travels more slowly across the face of the Sun, because it is much farther away from Earth.
  • Transits of Venus are among the rarest of predictable astronomical phenomena.They occur in a pattern that generally repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. 
  • Venus transits are historically of great scientific importance as they were used to gain the first realistic estimates of the size of the solar System.
  • Black Drop Effect: The strange ‘Black Drop Effect, was a concundrun that fouled the observations of interested and dedicated astronomists. At the moment when venus should nearly touch the edge of Sun, the circular planet appears elongated.

Some Important facts about Solar system


4.6 Billions years ago



Dwarf planets






Biggest planet


Biggest satellite


Blue planet


Green planet


Brightest palnet


Brightest planet outside solar system

Sirius (Dog star)

Closest star of solar system

Proxima centauri

Coldest planet


Evening Star


Farthest Planet from Sun


Planet with maximum number of satellite


Densest Planet


Fastest rotation in Solar System


Morning star


Nearest planet to earth


Nearest planet to sun


Red planet


Slowest revolution in solar system


Slowest rotation in solar system


Smallest planet


Smallest satellite


Earth’s twin


Only satellite with an atmosphere like earth


Fastest revolution in solar system


Hottest planet



Follow Us on Social Media

Follow us on Facebook

Send us your Feedback